Recently, as portable electronic instruments, such as portable computers, portable phones and camcorders, have been steadily developed so that they are downsized and lightened, lithium secondary batteries used as drive sources for the electronic instruments are also required to have a compact size and a light weight.
A lithium secondary battery includes a cathode, an anode and an electrolyte. Upon charge, lithium ions are deintercalated from a cathode active material. Then, the lithium ions are intercalated into an anode active material such as carbon particles, and are deintercalated from the anode active material upon discharge. In this manner, lithium ions transfer energy while they reciprocate between the cathode and the anode, thereby allowing the battery to be charged/discharged. However, quality of a lithium secondary battery may be degraded by the deterioration of an anode during repeated charge/discharge cycles. Also, when a battery is exposed to high temperature conditions, stability of the battery may be degraded by the gas generation in the battery.
To solve the aforementioned problems, EP 683537 and JP 08-45545 suggest a method for minimizing deterioration of an anode by using vinylene carbonate (referred to also as VC hereinafter) that forms a SEI film on an anode. However, the SEI film formed by VC shows a relatively high resistance and is decomposed with ease when exposed under high temperature conditions to generate gas such as carbon dioxide, resulting in degradation of the stability of a battery.